You don't need the app open. But that's besides the point. If you have not tried this, disconnect the fitbit app as your tracker and then reconnect it.
Also, if you are using the AARP app (AARP now), try deleting it, and reinstalling it. I was having a problem today getting credit for my steps (I use Apple Health), and after several chapters of frustration, deleted the app, re-installed it, and the steps were credited upon the re-install asking me to connect qa tracker, which I was able to successfully do.
One last thing...this system can be very funky. By accessing transaction history, make sure you haven't exceeded the allowed allotment of points earned for a day, which as most know is 7500. I've hit 7500 by mistake before the steps are completed and sometimes get the points later, sometimes don't.
If it ain't one thing, its something else...the AARP way of life.